This invention relates generally to memory systems and more particularly to memory systems which are adapted to store a periodic signal and recycle complete cycles of such stored periodic signal.
As is known in the art, it is sometimes desirable to receive a pulse of radio frequency energy and produce a continuous wave signal having a frequency related to the frequency of the received energy. Such continuous wave signal may, for eample, be transmitted as either a continuous wave signal or may be pulse modulated to enable transmission of a train of radio frequency signals. One technique suggested to produce such continuous wave signal has been to store the receive signal in a re-circulating memory; however, because the phase of the receive signal at the start of the pulse relative to the phase of the signal at the end of the pulse is generally not known, because the frequency of the signal is not known, a phase discontinuity may be produced during the recycling. This phase discontinuity distorts the continuous wave signal being produced and thereby reduces the effectiveness of the system. In another technique, this phase discontinuity problem is solved by producing control signals indicating the start of each cycle of the receive signal. Such technique is described in U.S. Pat. No. 4,223,404 "Apparatus for Recycling Complete Cycles of a Stored Periodic Signal" issued Sept. 16, 1982, to Oscar Lowenschuss and assigned to the same assignee as the present invention. Such system stores a slice of, or the complete radio frequency pulse, and then recycles complete cycles of the store signal. While such system is useful in many applications, in other applications it is desirable to recycle complete cycles of the received pulse prior to the termination of an arbitrary pulse slice thereof or the received signal itself.
Another system is described in my U.S. Pat. No. 4,380,816 issued Apr. 19, 1983 and assigned to the same assignee as the present invention. In this system, samples of a periodic signal are stored in the memory at a time commencing at the start of a cycle of the periodic signal. A first control signal is produced at the start of each cycle of the periodic signal and a second control signal is produced when a predetermined portion of the storage means is full. In response to the second control signal and one of the first control signals produced after the second control signal, a signal is produced indicating the portion of the memory having samples of complete cycles of the periodic signal stored therein, such indicating signal being related to the amount of samples stored in the predetermined portion of the memory plus the amount of samples stored in such memory between the time of the second control signal and the time of the first one of the first control signals produced after the second control signal. The samples in the portion of the memory having complete cycles stored therein as indicated by the indictating signal, are then recycled through the memory. While such apparatus is useful in many applications, in other applications a higher degree of accuracy is required in replicating the frequency of the periodic signal.